Since its introduction, third-generation (3G) cellular technology has provided the ability to deliver more voice channels and higher-bandwidths to user equipment/terminals (UEs) such as mobile handsets. In reality, however, while most 3G networks allowed for higher-quality voice services, the same did not apply to data speed.
In this regard High-Speed Packet Access (HSPA) was developed. HSPA is a protocol that provides a transitional platform for UMTS-based 3G networks to offer higher data transfer speeds, and so bridges the gap between 3G networks and the Internet. HSPA is made up of High Speed Downlink Packet Access (HSDPA) and High Speed Uplink Packet Access (HSUPA).
HSDPA provides impressive enhancements over WCDMA, including shorter connection and response times. More importantly, HSDPA offers three- to five-fold throughput increase, which translates into significantly more data users on a single frequency or carrier. The substantial increase in data rate and throughput is achieved by implementing a fast and complex channel control mechanism based upon short physical layer frames, Adaptive Modulation and Coding (AMC), fast Hybrid-ARQ (Automatic Repeat-reQuest) and fast scheduling. The exact implementation of HSDPA is known, and so will not be described further here.
HSPA can be implemented as an upgrade to and in co-existence with deployed UMTS/WCDMA networks. The cost of deploying HSPA chiefly lies in base station and Radio Network Controller (RNC) software/hardware upgrades. Most base stations (also known as Node Bs) will need upgrades to cope with the increased data throughput and the consequences of moving to a more complex protocol.
Advancements have also been made to HSPA since its introduction, and the improved version has been termed evolved HSPA (eHSPA). In this regard, an eHSPA Node B/Enhanced Node B has been proposed, which, in addition to its Node B functionally, includes RNC functionality. This enhanced Node B enables user terminals to use 3GPP Release 5 and later Release air interfaces with no modifications for HSPA traffic.
The RNC functionality is provided alongside the standard Node B functionality within the base station/eHSPA Node B. With this architecture the call set up delay can be reduced, as there is minimal latency associated with the communications between the RNC functionality and the Node B functionality, since they are physically in close association.
It has also been proposed to use Node Bs (namely eNode Bs) similar to eHSPA Node Bs in the Long Term Evolution (LTE) network, which is a 4G technology, currently in development.
It is to be appreciated that the eHSPA Node B architecture has been designed so as to handle packet switched data communications more efficiently, as the RNC within the eHSPA Node B is able to communicate directly with the Packet Switched (PS) Component of the Core Network. While this architecture and use of eHSPA improves efficiency for PS communications, it is also imperative that the architecture is compatible with other services, such as Multimedia Broadcast and Multicast Services (MBMS).
MBMS is an IP-based technology designed to more efficiently deliver multimedia (video, audio, and text) content over 3G radio and network resources. For Universal Mobile Telecommunications Systems (UMTS) it is a feasible platform for the delivery of multimedia services, as it allows many users to receive the same service simultaneously.
Before MBMS, multimedia content had to be delivered as IP packets via unicast transmission, where each individual user consumed network resources to download content, such as music or ring tones, and the resources were uniquely provided to that individual. MBMS now makes it possible to transmit data only once in each cell, and all interested users in the cell can share the cost of the radio resources consumed. This can be achieved either by broadcast, where all users receive the service, or by multicast, where only a selected set of users receive the service. Multicast is typically used to target users that have explicitly subscribed to a service.
Applications for MBMS include multimedia streaming and file downloads. Further, a multicast service received by a User Equipment/Terminal (UE) may consist of a single on-going session (e.g. a multimedia stream) or may involve several intermittent multicast sessions over an extended period of time (e.g. messages). An example of a service using the multicast mode could be a football results service for which a subscription is required.
The MBMS service has two transmission modes, namely Point-to-Point transmission (PTP) and Point-to-Multipoint transmission (PTM). In PTM, one common channel is used for all UEs in a cell, and in PTP, a separate channel is used for each UE.
While the eHSPA Node B can be incorporated into an LTE or a UMTS system, the standard MBMS procedure does not provide a practical compatibility with eHSPA. This is because in the current MBMS procedure, the “Session Start” message, which establishes the network resources needed for the MBMS data transfer, needs to be routed directly between the SGSN and all of the RNCs that it can connect towards. Therefore, in view of each eHSPA Node B incorporating a Radio Network Controller (RNC), this means that transport bearers are now also required to extend from the SGSN to each eHSPA Node B. This is undesirable, as it means more transport resources are required. It would greatly increase the traffic load on the Iu interface, and is also likely to cause a lot of problems for SGSN processor dimensioning and Iu-PS transport dimensioning. Therefore, in fact MBMS technology and eHSPA technology are completely at odds with each other.